1. Field of the Invention
The present invention relates to the field of oil field production equipment, and more particularly to items used in gas lift production operations.
2. Description of Prior Art
In hydrocarbon production, commonly the pressure in the reservoir being produced is not great enough to force the oil to the surface. The two most common methods used for bringing the oil to the surface are pumping and artificial or gas lift.
Gas lift utilizes the standard well configuration where there is an outer casing or annulus and an interior production tubing string. A seal is located above the casing perforation zone, where the hydrocarbons enter the casing, so that there is a closed volume between the casing and the production string above the seal. Below the seal the production string is open to allow the hydrocarbons to enter the production string. A gas lift operation involves forcing compressed natural gas down into the well bore into the fixed volume zone above the seal and around the outside of the production tubing and inside the casing.
Specialized devices called mandrels are positioned at various levels in the production string to allow the compressed gas to enter the casing. A mandrel generally has two parts. The first part is referred to as the tubing unit which is a modified piece of pipe similar to the pipe used in the production string The tubing unit has a port or series of ports to allow the compressed gas to enter the production string. The second part of a conventional mandrel is a valve lug which is attached to the tubing unit. The lug has a port or series of ports which are aligned with the port or series of ports in the tubing unit. The lug is further designed to hold a valve used in gas lift operations to control entry of the compressed gas into the production string and thereby cause a quantity of hydrocarbon fluid to move up the production tubing to the surface. The gas aerates the hydrocarbon fluid, which makes the fluid exert less pressure than the formation, so that the formation pressure forces the fluid to the surface. A common problem associated with gas lift operation is the corrosion and abrasion, which are generally referred to herein as erosion, to the ports in the mandrel by the compressed gas as it passes through the valve and enters the production string, and by the fluids and any incorporated impurities, such as hydrogen sulfide and sand, flowing in the production tubing.
There are two valve types which are commonly used, and they are referred to as fluid operated and pressure operated. Pressure operated valves are generally designed so that the flow path in the valve lug is parallel with the production tubing after the gas exits the valve. As a result, the major erosion location of a mandrel with a pressure operated valve is the port into the tubing unit. On the other hand, fluid operated valves generally have radial gas ports so that the gas exits perpendicular to the valve lug axis. The gas flow must then bend to allow the gas to traverse the port into the tubing unit. Erosion of the valve lug thus occurs opposite each valve port, as well as the erosion which occurs at the port into the tubing unit.
When a single mandrel erodes to the point of leaking, the entire production string must be pulled from the well and at least the damaged parts are replaced. Generally, when one mandrel is replaced, all the mandrels in the string are replaced to prevent pulling the production string for each mandrel failure. Pulling the production string and the replacement of all the mandrels is a large expense and so it is desirable to reduce the erosion rate of the mandrel and the frequency of pulling the production string and replacing the mandrels.
U.S. Pat. No. 4,567,954 discloses a tungsten carbide drill bit having a replaceable tungsten carbide nozzle for aiming the drilling fluids used when the bit is operating. The nozzle has an external threaded sleeve which is brazed on the nozzle and used &o allow the nozzle assembly to thread into the bit. Alternately, the nozzle is held in place by a snap ring.